The document U.S. Pat. No. 4,710,028 (EP-0 206 912) discloses a deviation meter making it possible to locate a missile flying at least approximately in the direction of a target and to which is linked an optical emitter generating successive light flashes in the near infrared, said deviation meter comprising:                an optical detector comprising a matrix of photosensitive elements able to detect said successive light flashes;        an optical system, which observes the scene in which the target and said missile are located and in the focal plane of which is positioned said optical detector;        electronic means of controlling said optical detector that are able to trigger snapshots of said scene by the latter; and        means able to synchronize snapshots of said optical detector with said successive light flashes.        
Thus, in such a known deviation meter, the position in said matrix of the photosensitive element or elements excited by said successive light flashes is representative of the position of said missile relative to the axis of said optical system.
When such a deviation meter is used in an alignment-guided missile firing station, it is associated with a daytime aiming device (telescope) and/or a nighttime aiming device (heat-sensitive camera) for the use of the operator of said firing station. There is thus obtained a composite aiming system with deviation meter enabling said operator to follow a target with one or other of said aiming devices depending on the conditions of brightness, the deviation meter supplying position information concerning the missile in flight to means of guiding the latter to said target.
In such a composite aiming system, there is therefore a deviation measurement channel and at least one aiming channel, each of said channels having its own optical system, its own detector and its own electronics (heat-sensitive aiming), and so on, which renders said system complex, costly, heavy and voluminous. Such drawbacks are particularly disadvantageous when said composite aiming system is to be carried by the operator.
These drawbacks of complexity, cost, weight and bulk are added to by the fact that it is necessary to provide, for the deviation meter channel, a wide-field optical channel for the control of the missile by the firing station after launch and a reduced-field optical channel for guidance.
Moreover, in such a composite aiming system, it is essential for performance purposes for the axes of the deviation measurement and aiming channels to be strictly harmonized and remain so throughout the duration of use, which entails precision adjustments or even an additional optical harmonization device, and means that the system has to be used with care, although the conditions of use do not normally allow that.
Furthermore, the daytime aiming device (telescope) forms a direct optical channel able to transmit a laser attack to the operator.
Finally, because, in such a composite aiming system with deviation meter, the missile is servo-controlled to the line of sight of the daytime aiming device or to that of the nighttime aiming device, the guidance of the missile is very sensitive to the untimely or ill-controlled movements that the operator imparts on said system (for example, when jettisoning the missile from its launch tube, when tracking a target with strong defilade, difficulties while aiming, etc.). The result is a disturbed guidance for the missile which, possibly, may even leave the field of said system.